VIP clipper and scaler II

Hi all,

I have design a video data path through clipper and scaler II:

CVI 1080P-> clipper -> scaler II 1080P -> CVO 1080P

the output resolution of the scaler II is set to 1920x1080.

the data path is working when the output of the clipper is Hx1080, the range of H is from 10 to 1920.

but once I change the the vertical pixel number, there is no output from the CVO.

I have read some posts here, one mentioned that I should add a frame buffer between the clipper and the scaler II. But in the design example an427 from altera, there is no buffer between the clipper and scaler II. I doubt that it is necessary to add a frame buffer.

the clocked video clock is 74.25 MHz and the avalon ST clock is 148.5 MHz

Thanks for your assistance!

Best Regards,

Daniel